U.S. patent number 6,172,985 [Application Number 09/014,726] was granted by the patent office on 2001-01-09 for automatic detection of pots line.
This patent grant is currently assigned to Gateway 2000, Inc.. Invention is credited to Timothy G. Gilbert.
United States Patent |
6,172,985 |
Gilbert |
January 9, 2001 |
Automatic detection of pots line
Abstract
The automatic detection of plain-old telephone system (POTS)
lines. A line-type detector detects the particular type of
communications line and preferably correspondingly configures a
communications device, depending on whether POTS was detected or
not. The detection is preferably accomplished by detecting the two
dial tone frequencies present in a POTS line.
Inventors: |
Gilbert; Timothy G.
(Vermillion, SD) |
Assignee: |
Gateway 2000, Inc. (North Sioux
City, SD)
|
Family
ID: |
21767335 |
Appl.
No.: |
09/014,726 |
Filed: |
January 28, 1998 |
Current U.S.
Class: |
370/465; 370/252;
370/389 |
Current CPC
Class: |
H04L
12/5692 (20130101); H04M 1/82 (20130101); H04M
3/22 (20130101); H04M 3/2272 (20130101); H04M
11/062 (20130101); H04Q 11/0471 (20130101); H04M
3/005 (20130101); H04Q 1/444 (20130101); H04Q
2213/13034 (20130101); H04Q 2213/13093 (20130101); H04Q
2213/13103 (20130101); H04Q 2213/13106 (20130101); H04Q
2213/13107 (20130101); H04Q 2213/13199 (20130101); H04Q
2213/13202 (20130101); H04Q 2213/13209 (20130101); H04Q
2213/13302 (20130101); H04Q 2213/1332 (20130101); H04Q
2213/13396 (20130101) |
Current International
Class: |
H04M
1/82 (20060101); H04L 12/28 (20060101); H04M
3/22 (20060101); H04M 11/06 (20060101); H04Q
11/04 (20060101); H04Q 1/30 (20060101); H04Q
1/444 (20060101); H04M 3/00 (20060101); H04J
003/16 () |
Field of
Search: |
;370/465,252,389,390,242
;709/249 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"AT&T V.32bis/V.32/FAX High-Speed Data Pump Chip Sets Data
Book", Published by AT&T Microelectronics, pp. 1-91, F1-F15,
B13 (Dec. 1991). .
"Introducing AIRplex", http://kiwi.futuris.net/kme/, Product
information from K and M Electronics, Inc., 1 page, (1995). .
"Kiss Cables Good-bye",
http://www.portablecomputing.com/premier/162 htm, Product review of
IBM cordless modem, 2 pages, (Apr. 8, 1997). .
Pargh, A., http://www.gadgetguru.com/aol/reviews/152.shtml, Product
review of IBM cordless modem, 2 pages, (1997). .
IBM Announcement Letters, http://www1.ibmlink.ibm.com/cgi-bi, 1
page (1995). .
"IBM's Waverunner Nominated for Networking Industry Awards `ISDN
Product of the Year`", M2 Presswire, M2 Communications, pp. 2-4
(Jul. 7, 1995). .
"Integrated Services Digital Network (ISDN) Basic Access Interface
for Use on Metallic Loops for Application on the Network Side of
the NT", American National Standard for Telecommunications
T1.601-1992, Cover page, pp. 49-50, (Feb. 21, 1992). .
"TMS320C3x", Texas Instruments User's Guide for Digital Signal
Processing Product No. TMS320C3x, Revision J, Cover page, Title
page and pp. 1.1-1.10 (Oct. 1994). .
"V:32bis/V.32/FAX High-Speed Data Pump Chip Sets Data Book",
Published by AT&T Microelectronics, pp. 1-91 (Dec. 1991). .
"WaveRunner Digital Modems",
http://www.pc.ibm.com/options/g2214076.htm1#dagtb, pp. 1-8 (1994).
.
Bryce, J.Y., "Using ISDN", Published by Que Corporation, Cover
page, Title page and Table of Contents (1995). .
Pearlstein, J., "Farallon Introduces Netopia ISDN Modem", MacWEEK,
vol. 10, No. 2, 1 page, (Jan. 15, 1996). .
Pearlstein, J., "ISU Express adds POTS to ISDN", MacWEEK, vol. 9,
No. 41, 2 pages, (Oct. 16, 1995). .
Tam, T., "Exploiting ISDN Services to the Fullest", PC Week, vol.
12, No. 3, 3 pages, (Jan. 23, 1995)..
|
Primary Examiner: Horabik; Michael
Assistant Examiner: Jones; Prenell
Attorney, Agent or Firm: Schwegman, Lundberg, Woessner &
Kluth, P.A.
Claims
I claim:
1. A computerized system comprising:
a) a computer having at least a processor and a memory; a
communications device operatively coupled to the computer, and
operatively coupled to a communications line of a particular
type;
b) a line-type detector operatively coupled to the communications
device to detect whether the particular type of the communications
line is a plain old telephone system (POTS) line, and
correspondingly configure the communications device, the line-type
detector further comprising:
i) a pair of circuitry, one circuitry specific to POTS, the other
circuitry specific to a communications line type other than POTS;
and
ii) a controller to switch between the pair of circuitry depending
on whether POTS was detected, the controller further
comprising:
A) a relay;
B) a relay control operatively coupled to the relay;
C) a modem controller operatively coupled to the relay control;
and
D) a modem digital signal processor (DSP) operatively coupled to
the modem controller.
2. The computerized system of claim 1, wherein the particular type
of communications line is selected from the group consisting of
plain-old telephone system (POTS), integrated services digital
network (ISDN), and asynchronous digital subscriber line
(ADSL).
3. The computerized system of claim 1, wherein the communications
device includes analog modem capability and terminal adapter
capability.
4. The computerized system of claim 1, wherein the line-type
detector is integrated into the communications device.
5. A communications device to couple a computer to a communications
line of a particular type comprising:
a pair of circuitry, one circuitry specific to POTS, the other
circuitry specific to a communications line type other than POTS;
and,
a controller to detect whether the particular type of the
communications line is POTS and correspondingly switch between the
pair of circuitry depending on whether POTS was detected, the
controller comprising:
i) a relay;
ii) a relay control operatively coupled to the relay;
iii) a modem controller operatively coupled to the relay control;
and,
iv) a modem digital signal processor (DSP) operatively coupled to
the modem controller.
6. The communications device of claim 5, wherein the controller
switches between the POTS circuitry and the other circuitry
incident to detection of at least one dial tone frequency.
7. The communications device of claim 6, wherein the at least one
dial tone frequency comprises a 350 Hz frequency and a 440 Hz
frequency.
8. A communications device to couple a computer to a communications
line of a particular type selected from the group consisting of
POTS and ISDN, the communications device comprising:
a POTS digital-analog adapter (DAA);
an TSDN NT-1 adapter;
a relay to switch between the POTS DAA and the TSDN NT-1 adapter;
and
a controller to detect the particular type of communications line
and direct the relay to switch accordingly, the controller
comprising:
a modem digital signal processor (DSP);
a modem controller operatively coupled to the modem DSP; and,
a relay control operatively coupled to the modem controller.
9. The communications device of claim 8, wherein the controller
detects at least one dial tone frequency and directs the relay to
switch accordingly incident to detection of the at least one dial
tone frequency.
10. The communications device of claim 9, wherein the at least one
dial tone frequency comprises a 350 Hz frequency and a 440 Hz
frequency.
11. A method for configuring a communications device for a computer
having a connector to operatively couple to a communications line,
the method comprising:
a) providing a line-type detector operatively coupled to the
communications device to detect whether the particular type of the
communications line is a plain old telephone system (POTS) line,
and correspondingly configure the communications device, the
line-type detector further comprising:
i) a pair of circuitry, one circuitry specific to POTS, the other
circuitry specific to a communications line type other than POTS;
and
ii) a controller to switch between the pair of circuitry depending
on whether POTS was detected, the controller further
comprising:
A) a relay;
B) a relay control operatively coupled to the relay;
C) a modem controller operatively coupled to the relay control;
and
D) a modem digital signal processor (DSP) operatively coupled to
the modem controller.
b) detecting whether the particular type of communications line is
a POTS line by detecting at least one dial tone frequency at the
connector;
c) initializing the communications device for POTS communication
upon detecting the at least one dial tone frequency;
d) detecting whether the particular type of communications line is
other than POTS upon failing to detect the at least one dial tone
frequency; and
e) switching to the circuitry specific to the communications line
type other than POTS and initializing the communication device for
a type of communication other than POTS.
12. The method of claim 11, wherein the at least one dial tone
frequency comprises a 350 Hz frequency and a 440 Hz frequency.
Description
FIELD OF THE INVENTION
This invention relates generally to the detection of a particular
type of communications line, and particularly to the automatic
detection of plain old telephone service (POTS) communications
lines.
BACKGROUND OF THE INVENTION
Remote communications have become increasingly popular in
conjunction with the use of computers. For example, a user may log
onto a network or the Internet through a modem plugged into a
communications line. This enables the user to access information
stored on the network, or access information stored on servers also
connected to the Internet.
In the past, remote access typically required that the user use an
analog modem to plug into a POTS communications line. Other
alternatives were not available. POTS communications is
advantageous in that POTS is nearly ubiquitous, but disadvantageous
in that it does not provide for high-bandwidth communications,
limiting its usefulness in voluminous data transfer applications
such as multimedia.
Recently, however, another alternative has become sufficiently
commonplace to be an adequate alternative to communications over a
POTS line. This alternative is ISDN. Communication over an ISDN
communications line requires a different type of device, what is
known within the art as an ISDN terminal adapter, or alternatively
an ISDN modem. ISDN communications is advantageous in that ISDN
provides for much higher bandwidth communications as compared to
POTS, but is disadvantageous in that it is still not nearly as
commonplace as is the ubiquitous POTS.
Therefore, a user desiring to having the best of both worlds is
forced to have both an analog modem for POTS communications, and a
terminal adapter for ISDN communications. Thus, when ISDN is
available, the user may take advantage of the higher bandwidth so
afforded, but still has POTS to fall back on when ISDN is not
available. This carrying of two devices is disadvantageous
especially for the portable computer user, who typically places a
premium on minimizing the weight of the equipment that must be
carried with the portable computer.
A more serious problem, however, is that the user may accidentally
plug a terminal adapter to a jack for a POTS communications line,
or a modem to a jack for an ISDN communications line. In the latter
case, the modem will likely just merely not work with the ISDN
line. However, in the former case, the terminal adapter may be
damaged as a result of it having been plugged into the POTS
line.
Therefore, there is a need for a communications device that is
amenable to both POTS and ISDN communications. There is a further
need for such a device to detect whether the device has been
plugged it into either a POTS or ISDN line, and configure the
device accordingly.
SUMMARY OF THE INVENTION
The above-mentioned shortcomings are addressed by the present
invention, which will be understood by reading and studying the
following specification. The invention describes the automatic
detection of POTS communications lines. A line-type detector
operatively coupled to a communications device in one embodiment
detects whether the particular type of communications line to which
the device has been coupled is POTS and correspondingly configures
the communications line. Preferably, the detection of POTS lines is
accomplished by detecting the dial tone frequencies that are always
present in a POTS line.
In this manner, a single communications device is operable in both
a POTS environment and a non-POTS environment, such as ISDN. A
portable computer user, for example, does not need to carry both an
ISDN terminal adapter and a POTS analog modem. The line-type
detector of the invention, when coupled to or integrated into a
suitable communications device, permits the device to interface
with both types of communications lines.
In different embodiments of the invention, computerized systems,
communications device, and methods of varying scope are described.
Still other and further aspects, advantages and embodiments of the
invention will become apparent by reference to the drawings and by
reading the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of a computerized system according to an
embodiment of the invention;
FIG. 2 is a block diagram of a communications device including a
line-type detector according to a preferred embodiment of the
invention; and,
FIG. 3 is a flowchart of a method to detect a communications line
type according to a preferred embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
In the following detailed description of the preferred embodiments,
reference is made to the accompanying drawings which form a part
hereof, and in which is shown by way of illustration specific
preferred embodiments in which the invention may be practiced.
These embodiments are described in sufficient detail to enable
those skilled in the art to practice the invention, and it is to be
understood that other embodiments may be utilized and that logical,
mechanical and electrical changes may be made without departing
from the spirit and scope of the present invention. The following
detailed description is, therefore, not to be taken in a limiting
sense, and the scope of the present invention is defined only by
the appended claims.
Referring first to FIG. 1, a diagram of a computerized system
according to an embodiment of the invention is shown. Computer 10
is coupled to monitor 12, pointing device 14, and keyboard 16.
Computer 10 includes a processor (preferably, an Intel Pentium
processor), random-access memory (preferably, at least sixteen
megabytes), read-only memory (ROM), and one or more storage
devices, such as a hard disk drive, a floppy disk drive, an optical
disk drive, and a tape cartridge drive. The invention is not
particularly limited to a given type of computer 10. Computer 10 is
preferably a PC-compatible computer such as those manufactured and
available from Gateway 2000, Inc., of Sioux City, S. Dak., and
running a version of the Microsoft Windows operating system. The
construction and operation of such computers are known within the
art. Computer 10 may be either a portable or a desktop computer, as
well.
Monitor 12 permits the display of information for viewing by a user
of the computer. The invention is not limited to any particular
monitor 12. Such monitors include cathode ray tube (CRT) displays,
as well as flat panel displays such as liquid crystal displays
(LCD's), and in one embodiment is a super-VGA CRT display. Pointing
device 14 permits the control of the screen pointer provided by the
graphic user interface of operating systems such as versions of
Microsoft Windows. The invention is not limited to any particular
pointing device 14. Such pointing devices include mouses, touch
pads, trackball, and point sticks. Keyboard 16 permits textual
entry into computer 10 as another input device to the computer, and
typically includes a plurality of alphanumeric keys, function keys,
navigation keys, cursor keys, and numeric keypad keys. However, the
invention is not so particularly limited.
Computer 10 is also operatively coupled to communications device
18. Communications device 18 as shown in FIG. 1 is an external
device to computer 10. However, the invention is not so limited,
and communications device 18 may also be an internal device, either
plugging into a slot within computer 10, or as a PCMCIA card
plugging into a corresponding PCMCIA card slot within computer 10.
Communications device 18 permits computer 10 to remotely connect to
a network or the Internet.
Communications device 18 has capability to communicate with at
least two types of communications systems 20, such as ISDN, POTS,
or asynchronous digital subscriber line (ADSL). POTS is also known
as public telephone switched network (PTSN). Preferably,
communications device 18 includes analog modem capability to
communicate over POTS, and a terminal adapter to communicate over
ISDN. Alternatively, communications device 18 includes what is
known in the art as ST interface capability to communicate over
ADSL. Other communications systems that are amenable to the
invention include other xDSL systems, such as high-speed digital
subscriber line (HDSL) and symmetric digital subscriber line
(SDSL). The invention is not limited in this regard. The
construction and operation of communications devices having the
ability to communicate over a single communications medium (e.g.,
only POTS, or only ISDN) are well known within the art. This
specification enables one of ordinary skill within the art to
modify such devices as described herein.
Communications device 18 has plug 22, which plugs into a
corresponding jack 24 of wall plate 26 as shown. Plug 22 and jack
24 typically are corresponding RJ-11 or RJ-45 plugs and jacks,
although the invention is not so limited. The same physically
appearing jack 24 may be used regardless of the type of
communications system 20 to which jack 24 is coupled; that is, the
physical appearance of jack 24 may not be indicative of the type of
line to which it is connected. For example, an RJ-45 jack may be
coupled to either an ISDN or a POTS line.
Therefore, communications device 18 includes an integral line-type
detector to determine the type of system 20 to which jack 24 is
coupled, and configures accordingly. For example, jack 24 of wall
plate 26 may be coupled to a communications line of a POTS
communications system 20. When jack 22 of device 18 is plugged into
such a jack 24, device 18 is able to detect when communications
system 20 is POTS, and correspondingly utilize its analog modem
capability. For further example, jack 24 of wall plate 26 may be
coupled to a communications line of an ISDN system 20. When jack 22
of device 18 is plugged into such a jack 24, device 18 is also able
to detect that communications system 20 is not POTS, and
correspondingly utilize its non-POTS capability, in this case, ISDN
capability as afforded by its terminal adapter capability.
The integral line-type detector of communications device 18
provides for a number of advantages. First, a computer user does
not have to have a separate device for each type of communications
system with which the computer may communicate. For example, rather
than having both a separate analog modem for POTS and a separate
terminal adapter for ISDN, only one device is needed. Second, the
computer user need not worry about possible damage that may result
when plugging in the wrong device into a given wall jack. For
example, plugging an ISDN terminal adapter to a jack for a POTS
line may permanently damage the adapter. The communications device
of the invention provides for a line-type detector that ensures
that this situation will not occur.
Referring now to FIG. 2, a block diagram of a communications device
including a line-type detector according to a preferred embodiment
of the invention. The device shown in FIG. 2 is able to detect
between a POTS and a non-POTS line, such as ISDN, and configure
accordingly. As described in conjunction with FIG. 2, the device
switches between POTS and ISDN. However, the invention is not so
limited, and the invention is amenable to the device switching
between POTS and another non-POTS line.
The incoming communications line from either ISDN or the POTS
includes two separate conductors 28a and 28b, as is normally found
in ISDN and POTS line installations. Conductors 28a and 28b are
coupled to either POTS digital-analog adapter DAA circuit 30 or
ISDN NT-1 circuit 32, as directed by double-pole, double-throw
(DPDT) switch 34. (Note that a two-conductor ISDN line is
communicatively coupled to a circuit 32 having what is known as a U
interface; ISDN is also available over a four-conductor line that
communicatively couples to a circuit 32 having what is known as an
ST interface.)
DPDT switch 34 is controlled by relay 36, which is itself
controlled by relay control 38. In a first default position, switch
34 normally directs conductors 28a and 28b to POTS DAA circuit 30
(i.e., when relay control 38 is not providing power to relay 36).
In a second position, relay control 38 provides power to relay 36
such that switch 34 directs conductors 28a and 28b to ISDN NT-1
circuit 32. Therefore, the communications line is at any given time
only coupled to either a POTS circuit (circuit 30), or a non-POTS
circuit, such as an ISDN circuit (circuit 32).
Relay control 38 is operatively coupled to conductors 28a and 28b.
Control 38 passes the signal detected on conductors 28a and 28b
onto modem controller 40. Modem controller 40 listens for two
frequencies that make up a dial tone on a POTS line, 350 Hz and 440
Hz. If controller 40 cannot detect both of these frequencies, it
directs relay control 38 to turn on relay 36, so that switch 34
directs conductors 28a and 28b to ISDN NT-1 circuit 32. If
controller 40 detects both of the dial tone frequencies, relay
control 38 is not directed to turn on relay 36, and switch 34
maintains its direction of conductors 28a and 28b to POTS DAA
circuit 30. Modem controller 40 is in one embodiment a TMS-320
controller available from Texas Instruments, Inc. Controller 40
desirably has analog inputs so that it is able to read POTS
signals.
Those of ordinary skill within the art will recognize that changes
may be made to the embodiment of FIG. 2 without departing from the
spirit or scope of the invention. For example, relay 36 with its
corresponding control 38 may be replaced by an electronic switching
apparatus that includes transistors and other electronic components
instead of the mechanical-oriented components such as relays as has
been described. In addition, the embodiment of the invention shown
in and described in conjunction with FIG. 2 switches between a POTS
and an ISDN communications line. However, the invention is not so
limited, and is amenable to switching between a POTS line and any
other non-POTS line.
Modem controller 40 also controls the operation of modem digital
signal processor (DSP) 42 in one of two modes. When controller 40
detects the presence of the POTS dial tone frequencies, it enters
DSP 42 into a POTS mode, such that DSP 42 sends data from the
computer to which it is coupled to the incoming communications
line, and vice-versa, over POTS DAA circuit 30, in a manner similar
to that performed by analog modems. When controller 40 does not
detect the presence of the POTS dial tone frequencies, it enters
DSP 42 into an ISDN mode, such that DSP 42 sends data from the
computer to the incoming communications line, and vice-versa, over
ISDN NT-1 circuit 32, in a manner similar to that performed by ISDN
terminal adapters. Controller 40 thus controls both the direction
of conductors 28a and 28b through switch 34 by control 38 and relay
36, to either circuit 30 or circuit 32, and also the mode in which
DSP 42 operates, either as an analog modem communicating with
circuit 30, or as a terminal adapter communicating with circuit
32.
DSP 42 is communicatively coupled to DAA circuit 30 and ISDN NT-1
circuit 32 via lines 31 and 33, respectively. Each line 31 and 33
preferably includes two or more conductors, such that each has
conductors corresponding to at least conductors 28a and 28b of the
incoming communications line. The ISDN NT-1 circuit 32, for
example, may communicatively couple DSP 42 via a four-conductor
line 33, in which case circuit 32 has an ST interface, or via a
two-conductor line 33, in which case circuit 32 has a U interface.
Furthermore, in one embodiment, controller 40 and DSP 42 are on the
same integrated circuit (IC), as is the case with the TMS-320
controller. In such instance, the combined chip, besides having
analog inputs, also includes DSP data pumps, and circuitry to
determine whether a (POTS) dial tone is present at the analog
inputs, as known within the art. The invention is not so
particularly limited, however.
POTS DAA circuit 30 and modem DSP 42 in its POTS mode together
constitute an analog modem, the construction and operation of which
are known within the art. U.S. Pat No. 5,452,289, entitled
"Computer-based multifunction personal communications system,"
which is hereby incorporated by reference, describes in detail the
operation of such modem technology and modem-based computerized
communications. DSP 42 in its POTS mode includes coder/decoder
(CODEC) functionality, which is typically a discrete component. DSP
42 in its POTS mode performs functionality such as modulation,
demodulation and echo cancellation to communicate over a POTS line.
DSP 42 in its POTS mode also performs digital to analog (D/A)
conversion, analog to digital (A/D) conversion, coding/decoding,
and gain control, as known within the art. DAA circuit 30 permits
the analog modem functionality provided by DSP 42 in its POTS mode
to connect to a preexisting POTS telecommunications system.
A detailed description of a DSP without CODEC functionality, a
separate CODEC, and a telephone interface (viz., a DAA) in direct
connection and cooperation with one another is described in the
publication entitled "AT&T V.32bis/V.32/FAX High-Speed Data
Pump Chip Set Data Book" published by AT&T Microelectronics,
December 1991, which is hereby incorporated by reference. The
AT&T data pump chip set described in this reference comprises
the core of an integrated, two-wire full duplex modem which is
capable of operation over standard POTS lines. The data pump chip
set conforms to the telecommunications specifications in CCITT
recommendations V.32bis, V.32, V.22bis, V.22, V.23, v.21 and is
compatible with the Bell 212A and 103 modems. Speeds of 14,400,
9600, 4800, 2400, 1200, 600 and 300 bits per second are supported.
This chip set consists of a ROM-coded DSP16A digital signal
processor U37 (viz., a DSP) and interface chip (viz., a DAA) U34,
and an AT&T T7525 linear CODEC U35 (viz., a CODEC). The
AT&T V.32 data pump chip set is available from AT&T
Microelectronics.
ISDN NT-1 circuit 32 and modem DSP 42 in its ISDN mode together
constitute an ISDN terminal adapter, or ISDN modem, the
construction and operation of which are known within the art. The
publication James Y. Bryce, Using ISDN, (Que Corporation: 1995),
which is hereby incorporated by reference, describes in detail the
operation of such modem technology and ISDN-based computerized
communications. DSP 42 in its ISDN mode performs functionality such
as data compression, data decompression, and error-checking, and
optionally functionality such as Multi Point-to-Point (PPP)
protocol compatibility. ISDN NT-1 circuit 32 performs the network
termination (NT)function necessary in ISDN lines; that is, it
permits the ISDN terminal adapter functionality provided in part by
DSP 42 in its ISDN mode to connect to a preexisting ISDN
telecommunications system.
A detailed description of the functionality of an NT-I is described
in the publication, "Integrated Services Digital Network (ISDN)
Basic Access Interface for Use on Metallic Loops for application on
the Network Side of the NT (Layer 1 Specification" published by the
American National Standards Institute, Inc. (ANSI) as approved on
Feb. 21, 1992, as ANSI T1.601-1992, which is hereby incorporated by
reference. This publication presents the electrical characteristics
of the ISDN basic access signals appearing at the network side of
the NT. It also describes the physical interface between the
network and the NT. The transport medium of the signal is a single
twisted-wire pair that supports full-duplex service.
Referring now to FIG. 3, a flowchart of a method to detect a
communications line type according to a preferred embodiment of the
invention is shown. The method is described in conjunction with the
preferred embodiment of the invention shown in FIG. 2; however, the
method is not so limited, and is applicable to other configurations
of the invention as well. From the starting point of step 44,
control proceeds to step 46, in which step a relay (such as relay
36 of FIG. 2) is by default closed to select POTS mode.
In step 48, the method attempts to draw a dial tone, which is
accomplished by listening for the two frequencies present in a POTS
dial tone, a 350 Hz frequency and a 440 Hz frequency. With respect
to the configuration of FIG. 2, this step is accomplished by the
modem controller 40. If a dial tone is present, control proceeds
from step 52 to step 54, and the communications device proceeds in
analog modem mode (e.g., DSP 42 of FIG. 2 receives and sends
communications signals through POTS DAA circuit 30 of FIG. 2), as
known within the art.
If a dial tone is not present, control proceeds from step 52 to
step 56, in which step the relay (such as relay 36 of FIG. 2) is
switched to select an alternative mode, such as ISDN, ADSL, etc.
The communications device then operates in this alternative mode in
step 58 (e.g., DSP 42 of FIG. 2 receives and sends communications
signals through ISDN NT-1 circuit 32 of FIG. 2, in the case where
the alternative mode is ISDN), as known within the art. From either
step 54 or step 58, control proceeds to step 60, at which step the
method is finished.
The automatic detection of POTS lines has been described. Although
specific embodiments have been illustrated and described herein, it
will be appreciated by those of ordinary skill in the art that any
arrangement which is calculated to achieve the same purpose may be
substituted for the specific embodiments shown. This application is
intended to cover any adaptations or variations of the present
invention. Therefore, it is manifestly intended that this invention
be limited only by the following claims and equivalents
thereof.
* * * * *
References